Adjustable-displacement gear pump

ABSTRACT

A positive displacement fluid pump capable of an output flow rate can be varied from a maximum to zero at a given pump rotation speed. The pump is a variable-fluid-displacement-volume, gear pump having complement elements associated with pumping gears to provide end seals for a variable-length pumping chamber. A timing arrangement maintains both pumping gears always in synchronization, whether engaged or fully disengaged (zero pump output). And a follower provides effective sealing with a movable face of an axially-translating pumping gear.

RELATED APPLICATIONS

[0001] This application claims priority to application Ser. No. 60/168,362, filed Dec. 1, 1999, and directed to an ADJUSTABLE-DISPLACEMENT GEAR PUMP.

BACKGROUND

[0002] 1. The Field of the Invention

[0003] This invention relates to hydraulic and other fluid pumps capable of a variable fluid throughput rate with respect to a given input rotational velocity. More particularly, the invention relates to novel systems and methods for controlling the volumetric displacement of gear pumps.

[0004] 2. The Background Art

[0005] Hydraulic pumps have been a key component of all hydraulic actuation systems for many years. Often, a hydraulic pump may be matched with one or more hydraulic motors. The hydraulic pump transfers energy to a working fluid. The hydraulic motor removes energy from the working fluid.

[0006] Currently, diaphragm, as well as vane, pumps are known in the art. Solid impeller pumps are used in circumstances that may not require positive displacement. For positive displacement, three common types of hydraulic pumps are used.

[0007] Vane pumps sweep fluid ahead of a vane mounted on a hub eccentrically positioned within a chamber. Vanes are urged toward an outer surface. Meanwhile, the vanes against the outer surface, are continually closing and opening chambers cyclically. The vane's extension toward the outer surface changes with the eccentricity of the hub with respect to the outer chamber, sweeping fluid in and out of ports positioned in the outer surface, or otherwise accessing the space between the hub and the outer surface.

[0008] Diaphragm pumps and piston pumps operate with one moving wall to draw a selected volume into a chamber. Then, using valves to control input and output ports, the moving wall (piston or diaphragm) of such pumps drives the working fluid into an output line. New developments in piston hydraulic pumps have made piston pumps extremely popular, as evident by the quantity in operation. In one piston pump type, a crank shaft is replaced by a driven shaft and a crank plate or “swash plate” that drives substantially orthogonally extending connecting rods for each piston. Such an apparatus has conventionally been associated with the manufacturer Sundstrand.

[0009] Finally, gear pumps are known in the art. Typically, spur gears sweep the space between teeth thereon through a cavity containing each gear. The cavity typically provides an axially oriented seal at the perimeter of the gear teeth. With the two gears mated together at a central contact position, hydraulic fluid may be sealed against completing a full circle with either gear.

[0010] For example, an input side of gears may move past an input port having access to the gears separating from contact with one another. At the input port location, the gear teeth are moving out of engagement and into their respective, circular, surrounding cavities. Oil (a typical working fluid) is swept with each tooth, filling the space between that tooth and its predecessor tooth moving along a rotary path.

[0011] As the gears each make a full rotation, the gears once again mesh, forcing oil out from between the teeth. Meanwhile, each contact line between the teeth forms a seal prohibiting, or greatly restricting, passage of working fluid back through from the outlet side to the inlet side of the contact region of the gears.

[0012] In the process of operation, a gear pump of a conventional design does not permit any variation in the pump displacement for each revolution of a pump. In more recent times, offsetting pump gears from one another in an axial direction has been postulated as a method of varying pump displacement and throughput. However, sealing the pumping region remains a continuing problem.

[0013] For example, conventional gear pumps maintain sealing between an end of a gear and a wall of a containment chamber. Clearances are typically very close, sufficient to maintain a virtually complete liquid seal. Upon relative axial movement of gears, the mating gears each may have an open cavity at one end thereof. This cavity must be filled or the pump has communication from a high pressure side to a low pressure side of each gear.

[0014] What is needed is a gear pump providing axial displacement of pump gears with respect to one another, with a close follower maintaining an end seal for each gear. A close follower may be a fixed wall for a gear that does not move axially. However, in the case of the gear that moves axially, the follower must follow closely enough to an end face of a moving gear to provide a liquid seal.

[0015] Meanwhile, each gear needs a complement to provide an end seal for a pump cavity having a variable length. That is, to the extent that a region of pump gear engagement is reduced, a liquid seal needs to be provided in the axial direction of each gear to close off the engaged (fluid driving) portion of the gears from the non-engaged portion of the gears.

[0016] A complement is needed to fill in the space between teeth in the disengaged regions of the gears. A variable displacement gear pump having close followers that always remain positioned sealingly proximate the end of a moving gear face, and having a complement on each gear to fill in the voids between teeth in order to present pseudo-walls defining a length of the active cavity (engaged or pumping region of a gear) is needed. Such a configuration has not been found in the prior art. A great advance in the art would provide an ability to vary displacement of a gear pump through a full range from zero (idling, no pumping occurring) at operational rotational speeds, to 100 percent of a maximum capacity when the gears are engaged to their maximum extent.

[0017] In the art, Applicant has not found any operable design for a gear pump capable of variable displacement, varying between no output flow and a full output flow, at a given pump rotational rate. Moreover, such a performance characteristic has not been found for any control mechanism for a gear pump.

[0018] An additional desired characteristic in a variable displacement pump would provide for a reduced amount of energy being applied to the working fluid during conditions when the pump is configured for reduced output. Producing a reduced overall pump output by redirecting pump output, such as in a load bypass or recirculating circuit, still undesirably applies energy from the pump to the working fluid. The working fluid is continually undergoing work in such a recycling pump arrangement, and thereby suffers from premature wear. This work creates unnecessary heat and draws unnecessary energy from the source of the rotational power. It would be an advance in the art to provide a pump capable of: (1) a variable output; (2) a reduced stress on the working fluid; and (3) more energy efficient during pump operation under low flow, or no flow, conditions.

[0019] Moreover, it would be an advance in the art to provide such a functionality in a gear pump by providing a timing gear that maintains synchronization between the two pumping gears, even when the pumping gears are not engaged. Thus, it would be an advance in the art to provide a variable displacement gear pump having complements associated with gears to provide end seals, a timing arrangement for maintaining both gears always in synchronization, whether engaged or fully disengaged (zero pump output), and a follower that remains close enough to a movable face of an axially-translating gear of a gear pump to provide effective sealing of the working fluid from passing therebetween.

BRIEF SUMMARY OF THE INVENTION

[0020] In accordance with the invention as embodied and broadly described herein, an apparatus and method are disclosed in suitable detail to enable one of ordinary skill in the art to make and use the invention. In certain embodiments, an apparatus and method in accordance with the present invention may include a case or pump housing, a pair of mated, rotating, mutually engaging gears. Both gears having a complement that substantially seals a variable length end portion of the gear from an engaged portion of the gear.

[0021] The gear pump may have followers, including solid members through which supporting axles of each respective gear may pass, as appropriate. A follower typically maintains a substantially complete, operational, fluid seal between a portion of itself and an end face of a pump gear. A follower that always maintains an effective seal between a portion of itself and a corresponding gear end face may be characterized as a close follower.

[0022] The apparatus may include a timing gear located remotely from an axially fixed gear. The timing gear maintains synchronization between the axially translating gear and the axially fixed gear. Such synchronization allows the axially translating gear to engage selectively with the axially fixed gear.

[0023] An exemplary adjustable displacement gear pump is capable of a variable fluid output between a maximum flow rate and zero flow at a constant drive shaft speed. One embodiment provides complement elements associated with a pair of pumping gears, the complement elements being portions of end seals for a pumping chamber having a variable length between a maximum length and zero length. The chamber length may be characterized as a distance between a proximal pumping chamber end seal and a distal pumping chamber end seal.

[0024] Also present is a timing arrangement for maintaining both pumping gears always in synchronization, whether the pumping gears are engaged or fully disengaged. A stationary close follower provides effective sealing with a fixed face of an axially fixed gear. A movable close follower provides effective sealing with a movable face of an axially translating pumping gear. A means to vary the pumping chamber length from a maximum length to a zero length provides a way to control pump output.

[0025] A pump may further include a metering valve arrangement between structure of a follower and structure associated with fluid input and output ports. The metering valve would operate to further control pump output during conditions of reduced pump chamber length.

[0026] One presently preferred timing arrangement uses a timing gear having a similar cross-section to a first of the pumping gears. The timing gear may typically be oriented in axial alignment, maintained in meshing agreement with, and spaced apart axially from the first pumping gear. The meshing agreement allows a second of the pumping gears, while meshed with the first pump gear, to be axially translated to mesh with the timing gear. Whenever the second gear is axially translated out of mesh with the first gear, the timing gear maintains synchronization of the gears such that the second gear may be axially translated back into mesh with the first gear. A timing arrangement may even be located exterior to a pump housing. Any convenient way to maintain synchronization between pumping gears may be adequate for the practice of certain embodiments of this invention.

[0027] The first chamber end seal typically includes a distal end of a first complement and structure associated with a movable close follower. The movable, close follower substantially seals with a proximal end of a first pumping gear. The first complement is typically carried by structure associated with the movable close follower for axial translation in substantially sealed sliding engagement with an exterior surface of a second pumping gear.

[0028] The second chamber end seal includes a stationary close follower. A close follower may be one of various structures, such as a proximal end of a sleeve center, a portion of a proximal end of a housing bridge structure, and a portion of a proximal end of a second complement. The second complement is typically fixed in place axially in rotatable engagement with structure of a pump housing and in slidable concentric engagement with the first gear. The second complement functions to allow axial translation of the first gear while substantially maintaining a fluid seal therebetween.

[0029] One embodiment of a pump, according to the present invention, may typically include means to vary the pump chamber length from a maximum length to zero length. One way to accomplish changes in chamber length may include applying differential hydraulic pressure between proximal and distal ends of a piston structure to control axial displacement of the first pumping gear. Suitable piston structures may generally include a follower assembly carrying the first gear.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The foregoing and other features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only a typical embodiment of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:

[0031]FIG. 1 is a perspective view in elevation, partially in section, of an apparatus in accordance with the invention;

[0032]FIG. 2 is an exploded, perspective assembly view of the internal operating elements of the apparatus of FIG. 1;

[0033]FIG. 3 is a side, elevation, cross-sectional view taken through a midplane of the apparatus of FIG. 1;

[0034]FIG. 4 is a front, cross-sectional, elevation view taken through the plane 4-4 indicated in FIG. 3 and looking in the direction of the arrows;

[0035]FIG. 5 is a front, cross-sectional, elevation view taken through the plane 5-5 indicated in FIG. 3 and looking in the direction of the arrows;

[0036]FIG. 6 is a front, cross-sectional, elevation view taken through the plane 6-6 indicated in FIG. 3 and looking in the direction of the arrows;

[0037]FIG. 7 is side, elevation, cross-sectional view of the internal operating elements of the apparatus of FIG. 3, where the operating elements are arranged in an approximately full flow configuration;

[0038]FIG. 8 is side, elevation, cross-sectional view of the internal operating elements of the apparatus of FIG. 3, where the operating elements are arranged in an approximately half-capacity flow configuration;

[0039]FIG. 9 is side, elevation, cross-sectional view of the internal operating elements of the apparatus of FIG. 3, where the operating elements are arranged in a greatly reduced flow configuration;

[0040]FIG. 10 is side, elevation, cross-sectional view of the internal operating elements of the apparatus of FIG. 3, where the operating elements are arranged in a zero flow configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041] It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of embodiments of the system and method of the present invention, as represented in FIGS. 1 through 10, is not intended to limit the scope of the invention. The scope of the invention is as broad as claimed herein. The illustrations are merely representative of certain presently preferred embodiments of the invention. The invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

[0042] Those of ordinary skill in the art will, of course, appreciate that various modifications to the details of the Figures may easily be made without departing from the essential characteristics of the invention. Thus, the following description of the Figures is intended only by way of example, and simply illustrates certain presently preferred embodiments consistent with the invention as claimed.

[0043] Referring to FIG. 1, a pump assembly, generally indicated at 10, is illustrated. The pump 10 typically includes a drive shaft 12, which may be rotated in either direction, as indicated by circumferential double-headed arrow 14. In the pump 10, reversing the direction of rotation of the drive shaft 12 merely reverses the direction of fluid flow through the pump 10. That is, intake and output ports (not shown) of the pump 10 are determined by the direction of rotation of the drive shaft 12.

[0044] As illustrated in FIG. 1, the drive shaft 12 carries a pump gear 16 in driving relation at an axially fixed position along the drive shaft 12. A complement 17 fits the toothed surface of gear 16 in a substantially sealed, slidable, relation. Taken together, the complement 17 and gear 16 form a substantially solid circular cross-section. Spaced apart axially from the gear 16, and also carried in driving relation by the drive shaft 12, is a timing gear 18. Gears 16 and 18 may have identical cross-sections and are mounted in meshing alignment on the drive shaft 12.

[0045] A sleeve center 20 receives the drive shaft 12 in a sealed and load-bearing relationship, and also serves as a spacer between the gears 16 and 18. The sleeve center 20 has a maximum radial dimension in agreement with a maximum radial dimension of the gears 16 and 18. Alternatively, the sleeve center may be a solid extension of a receiver housing 36. A sleeve 22 is constructed to circumscribe and slide over the sleeve center 20. The inside bore surface of the sleeve 22 provides a wiping, sealing surface for teeth carried by the gear 16. A follower 24 and the sleeve 22 together form a follower assembly 25.

[0046] The follower 24 provides a structural base from which to cantilever an idler axle 26. The axle 26 is typically fixed in position within the follower 24 by a press-fit, although other mounting methods are also conceivable. An idler gear 28 is carried in a rotatable bearing relationship by the axle 26. A portion of the distal face of the follower 24 forms a seal with the proximal end of the idler gear 28. Therefore, the follower 24 is a close follower to the idler gear 28.

[0047] Gears 16 and 28 have meshing tooth profiles, and may typically be identical in cross-section. Gears 16 and 28 need not be identical, although such a configuration simplifies manufacturing by reducing the pump parts count, and reducing costs.

[0048] A gear complement 30 receives the idler gear 28 in an axially sliding relation, and provides a substantial seal on the idler gear 28 surface against fluid flow in an axial direction. A slot 31 (FIG. 3) may be provided on the distal end of axle 26. The slot 31 functions to hold a split ring (not shown), and maintain the gear 28 in position on the axle 26. Other retaining structure, such as keys, sleeves, pins, splines, and so forth, may also be conceivable.

[0049] Continuing to refer to FIG. 1, a sender housing 32 may be essentially a solid block having an internal sender cavity 34. In the illustrated embodiment, the cavity 34 extends completely through the housing 32. It may be formed by two parallel, intersecting bores. The resulting cavity 34 has a cross-section that approximates a numeral 8, or is peanut shaped. The follower assembly 25 is received in the cavity 34 in an axially sliding, substantially sealed relationship.

[0050] The receiver housing 36 is similar to the sender housing 32 in that it also may be formed by two intersecting bores to form a receiver cavity 38. However, additional dividing structures including the sleeve center 20 and others not shown in FIG. 1 are also present in the receiver cavity 38. The receiver cavity 38 receives the sleeve 22 in an axially sliding, substantially sealed relationship. As the follower assembly 25 is moved, from the illustrated position toward the receiver housing 36, the gear 28 correspondingly moves into the receiver cavity 38. The receiver cavity 38 may be constructed to provide a portion designed to receive the gear 28 in an axially slidable, bearing relation.

[0051] For convenience, the pump 10 and its elements will be described with reference to orientations defined by a proximal end 48 and a distal end 50 of the pump 10. The sender housing 32 is axially sealed on the proximal end 48 of the pump 10 by a cap plate 40. The distal end of the sender housing 32 seals against a proximal end of the receiver housing 36. The distal end of the receiver housing 36 is axially sealed by a cap plate 42.

[0052] A set of alignment holes 44, passing completely through both cap plates 40 and 42 and housings 32 and 36, in the illustrated embodiment, are provided to assist in assembly of the pump 10. Another set of holes 46, also passing completely through both cap plates 40 and 42 and housings 32 and 36, receive tension bolts (not shown). The tension bolts carry the axial load required to maintain a fluid seal between all of the pump housings (32 & 36) and cap plates (40 & 42).

[0053] Referring to FIG. 2, additional details of construction of the pump 10 are illustrated. The follower 24 has a hole 54 in which is received the axle 26. A bore 56 in the follower 24 receives the complement 17 in a substantially sealed, rotating relationship. The complement 17 is restrained from axial displacement from the bore 56 by a suitable retainer, such as a snap ring (not shown) located in a groove 57. The rotatable seal prevents significant fluid escape from the sender cavity 34 (FIG. 1) between the bore 56 and the complement 17.

[0054] The inner surface of the complement 17 fits in sealing relation to the toothed surface of the gear 16. The complement 17 is sized to have a thickness to fit between the snap ring and the distal face of the follower 24. Such a thickness provides a sealing surface on its distal face being oriented in a plane at the distal face of the follower 24.

[0055] As illustrated, a portion of the proximal end of the sleeve 22 maintains the complement 17 in registration between the retaining snap ring at the groove 57 and the distal face of the follower 24. The follower 24, in combination with the complement 17 and a cross-section through the gear 16, essentially forms a sliding and sealing plug in the sender cavity 34. The proximal end of a pumping chamber (FIG. 7, denoted by area 104) is defined by the alignment and seal provided by the distal ends of the follower 24 and the complement 17.

[0056] Continuing to refer to FIG. 2, the interface between the gear 16 and the sleeve 22 may be readily visualized. A bore 58 is sized to fit the perimeter of the gear 16. The bore 58 receives teeth of the gear 16 in a sliding, wiping, sealed relation. The sleeve center 20 also is sized to slidingly seal against the bore 58 of the sleeve 22.

[0057] One way to attach the sleeve 22 and the follower 24 is illustrated as a set of pins 60. In the illustrated apparatus, the pins 60 may be press-fit or otherwise secured to a depth of about half their length into a set of receiving holes 62 in the sleeve 22. The remaining portions of the pins 60 are received in a suitable supporting relation (e.g. a press fit) into corresponding receiving holes (not shown) in the follower 24. Alternate methods for forming the resulting structure may be used, including welding the components together, or machining the follower assembly 25 (FIG. 1) from solid stock.

[0058] Referring now to FIG. 3, additional structural details of the construction of the pump 10 will be described. FIG. 3 is a side elevation view of a cross-section taken approximately through a midplane of the pump 10. The drive shaft 12 drives the gear 16, which in turn drives the idler gear 28. A single gear tooth face 74 located at the top of the gear 16 is visible in the Figure. A corresponding gear tooth face 76 is illustrated at the top of the timing gear 18. FIG. 3 illustrates how the gears 16 and 18 are oriented in meshing alignment, with gear teeth of both gears being located at identical azimuths relative to the drive shaft 12. In the configuration depicted in the illustration, a second gear tooth 76 is also visible at the bottom of the gear 18. A tooth of the gear 28 (shown in cross-section) obscures most of the tooth located at the bottom of gear 16.

[0059] Still referring to FIG. 3, the receiver housing 36 is shown to have a bridge element 78 that serves to form a sealing and supporting structure. To facilitate manufacturing, a bridge element 78 may be formed as an insert, press-fit or otherwise fastened to the receiver housing 36. A portion of a proximal end of the bridge 78 receives the complement 30 in rotating and sealing relation.

[0060] The complement 30 is seen, in the illustration, to be prevented from axial motion by a shoulder 79 in the proximal end of the housing 36 (including the bridge element 78) in combination with the distal end of the sender housing 32. The shoulder 79 prevents motion of the complement 30 toward the distal end of the pump 10 and is spaced from the proximal end of the receiver housing 36 by the thickness of the complement 30.

[0061] The gear 28 may slide axially through the complement 30 while substantially maintaining a fluid seal therebetween. It may now be realized that the bridge element 78 may have a length, extending from the proximal end of the receiver housing 36, that is shorter than illustrated. A minimum length for the bridge element 78 may be selected to be sufficient to provide a portion of the rotatable seal between the receiver housing 36 and the complement 30 at the proximal end of the receiver housing 36. However, the bridge element 78 may reasonably have a minimum length equal to the axial thickness of the complement 30. The complement 30 may be sufficiently retained axially by the shoulder 79 in the receiver housing 36 separate from any supporting contribution from the bridge element 78.

[0062] The proximal face of the complement 30, a cross-section through the gear 28, and the proximal face of the receiver housing 36 cooperatively form a substantially planar sealed surface. The plane containing the proximal faces of the complement 30, bridge element 78, and sleeve center 20, defines a sealed region with the distal end of the gear 16. This collection of elements may therefore be regarded as a close follower to the gear 16. In this case the close follower is axially stationary.

[0063] Further in reference to FIG. 3, a bushing 80 ray provide a sealed bearing support to the shaft 12 passing through the cap plate 40. A similar bushing 82 may be provided in the cap plate 42. On the subject of sealing, note that the illustrated embodiment is simplified to present certain inventive concepts. It is recognized that additional sealing elements may prove useful. For example, various surfaces, such as the parting line between housings 32 and 36, may be effectively sealed with o-rings or gaskets, including adhesives, silicones, shellacs, and the like, which are not shown. Various wiping seals may also be employed throughout, as on gear teeth, or shafts and rotating surfaces. Such details are generally known, obvious variations of the illustrated embodiments need not be catalogued herein.

[0064] Continuing to refer to FIG. 3, note that no structure is illustrated with which to move the follower 24 and associated structure such as the gear 28. Methods and mechanisms for moving such structure back and forth are generally known. Appropriate methods to move the pump structures back and forth include applying differential hydraulic pressure between proximal end of the cavity 34 and the distal end of the cavity 38. A metering valve may be installed in-line with the pump output stream, or in association with an independent high pressure source, to direct fluid to the desired cavity as required. Internal pump structure may then act as a variable position piston in such case. Mechanical linkages including elements such as push rods and jack screws being operated by various mechanical, manual, and electrical actuators may also be employed. Various combinations of mechanical and hydraulic elements may also be employed to advantage.

[0065] Reference will now be made to FIG. 4, a cross-section through section 4-4 in FIG. 3. The follower 24 fits in sealing relation along the profile of the cavity 34 (see also FIGS. 1 and 3). The follower 24, a cross-section through the shaft 26, the complement 17, and a cross-section through the gear 16 and drive shaft 12, effectively act in concert as a slidable stopper in the sender cavity 34. A keyway 84 is shown as one way to transfer power from the shaft 12 to the gear 16 without allowing the gear 16 to slip relative the drive shaft 12. Recall that the gear 16 is axially fixed in place, and that the complement 17 may slide in sealed relation along the gear 16. It can now be visualized that this “stopper” assembly functions as a moving wall, and defines one movable wall of the pump chamber (FIG. 7, denoted by area 104).

[0066]FIG. 5 is a cross-sectional view in elevation through section 5-5 in FIG. 3. FIG. 5 shows additional details of the pump chamber. For convenience, directions of rotation of the gears 16 and 28 are assigned, and are indicated by arrows 86 and 88. Teeth of the gears 16 and 28 are seen to be in wiping sealed relation with respect to the sleeve 22 and the sender cavity 34. Under the illustrated conditions, a low pressure zone 90 is created where teeth of the gears 16 and 28 rotate out of mesh. The low pressure area 90 is accessed for fluid supply by an input port 92. A high pressure zone 94 is created where the gear teeth come into mesh. The high pressure zone 94 is in open fluid communication with an exhaust port 96.

[0067] Referring to FIG. 6, a cross-sectional view in elevation through the section 6-6 in FIG. 3 illustrates a fixed wall of the pump chamber. The receiver cavity 38 is sealed by structure including the sleeve 22, the sleeve center 20, the drive shaft 12, the bridge element 78 of the receiver housing 36, the complement 30, the gear 28, and the axle 26. The sleeve 22 and gear 28 move axially in sealed relation with the remaining structure. This arrangement provides a fixed wall forming a sealing plane defining the distal end of the pump chamber.

[0068] Referring now to FIGS. 7-10, the change in length of the pump chamber 104 is illustrated. FIGS. 7-10 illustrate cross-sectional side views in elevation of selected internal operating elements of the pump 10 according to the present invention. Notably, the cap plates 40 and 42 and the sender housing 32 are not illustrated in these Figures. In FIG. 7, the elements are arranged in a position to define the maximum pump chamber length 104. Note that the complement 17 is located at the proximal end of the gear 16. FIG. 8 illustrates an arrangement to provide approximately a one-half the maximum flow rate per revolution. Note that the follower 24 has been displaced toward a distal end 106 of the receiver housing 36, and the complement 17 is approximately at mid-span of the gear 16.

[0069]FIG. 9 illustrates an arrangement that provides a substantially reduced flow rate compared to the maximum flow rate. In this circumstance, the follower 24 is displaced an additional amount toward the distal end 106, compared to the position illustrated in Figure 8. Note also that distal end of the gear 28 has come into engagement with the timing gear 18. Of note also, the distal end of the follower 24 is approaching the distal end of the sender housing 32 (not shown in FIGS. 7-10, see FIG. 1 or 3). The distal end of the follower 24 may obscure the opening of either or both of the ports 92 and 96 (see FIGS. 3 and 5). In this circumstance, the follower 24 may interact with a particularly formed and cooperative structure of the ports 92 and or 96 to also form a metering valve or orifice. Such a metering valve may come into actuation at the lower flow configurations of pump structure. Such an arrangement may also enable controlled relief of pressure in closed regions between teeth as closed in by other intermeshing teeth.

[0070]FIG. 10 illustrates a zero flow arrangement of pump elements. In this circumstance, the pump “chamber length” 104 is effectively zero. The distal end of the complement 17 is illustrated in contact with the sleeve center 20, and no free volume in which to transfer fluid exists in the pump chamber. The gear 28 may be completely disengaged, moving in an axial direction away from the gear 16. The full length of the timing gear 18 is now engaged by the gear 28, and maintains orientation of the gear 28 relative to the gear 16.

[0071] The illustrated example of the pump 10 has the drive shaft 12 axially fixed relative to the housing elements 32 and 36, and the movable idler axle 26 carried by the follower assembly 25 (FIG. 1). It is within contemplation to provide an idler axle, axially fixed in position, and a movable drive shaft. By way of example, the axle 26 may be lengthened to protrude from one or both cap plates 40 and 42. In such a configuration, pump flow rate may be controlled either by displacing the entire pump housing relative to the drive source, or by fixing the pump in place and moving the driving source (typically a motor) relative to the pump housing.

[0072] Certain other modifications to the illustrated apparatus 10 are also within contemplation, including without limitation, forming a secondary pump within the receiver cavity 38. This secondary pump may easily be formed by engagement of the timing gear 18 and the gear 28. With reference to FIG. 3, the timing gear 18 may be moved from its illustrated position to place its proximal end in sealing relation with the distal end of the complement 30. The gear 28 may be lengthened to always engage the gear 18.

[0073] A third complement, similar to the complement 30, may form a distal seal to the newly created secondary pump chamber. The sleeve center 20 may then be formed as two sleeve centers disposed on opposite sides of the gear 18. The sleeve 22 and the receiver cavity 38 may be appropriately lengthened to accommodate the increase in length of gear 28 and to allow full range in length of the main pump chamber. The secondary pump output may be used as a pressurized fluid source to control the length of the main pump chamber.

[0074] Pump elements may be formed from any appropriate materials, including, without limitation, ferrous and nonferrous metals, and engineered plastics or polymers. Depending upon output pressure requirements, working fluids, and desired pump life, pump gears may advantageously be formed from stainless steels, cast iron, or engineered plastics and the like. Seals may be formed throughout the pump structure by closely fitting the illustrated components, or by way of strategically added sealing elements. Housings may alternatively be formed with integral caps and assembled like opposed cups. A housing may also alternatively be structured as one deep vessel having a single lid on a single open end. Such construction details may be driven by manufacturing concerns.

[0075] In summary, it will be appreciated that the present invention provides a positive displacement pump having a variable output flow. The instant pump is a gear pump capable of varying its displacement, and therefore its output at a given rotation rate. The instant gear pump provides axial displacement of pump gears with respect to one another, and includes a close follower to maintain an end seal for each gear. A complement is included to provide an end seal for a pump cavity having a variable length. To the extent that an engagement region of the pump gear is reduced, a liquid seal against leakage in the axial direction past each gear closes off the engaged (fluid driving) portion of the respective gears.

[0076] The instant pump provides an ability to vary displacement of a gear pump through a full range from zero (idling, no pumping occurring) at operational rotational speeds, to 100 percent of a maximum capacity when the pumping gears are fully engaged to their maximum extent. Furthermore, the instant gear pump provides a timing gear to maintain synchronization between the two pumping gears, even when the pumping gears are not engaged.

[0077] The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes within the meaning and range of equivalency of the claims are to be embraced within their scope. 

What is claimed and desired to be secured by United States Letters Patent is:
 1. A pump having a positive displacement per cycle that is continuously variable between a maximum flow rate and a zero flow rate comprising: a housing; a first driven gear rotatably movable with respect to the housing; a second gear rotatably movable with respect to the housing and meshing with the first gear, wherein the first and second gears are axially movable relative to each other; a first complement, secured to rotate with and slide axially along the first gear; a second complement, secured to rotate with and slide axially along the second gear; a movable follower sealably engaged to the first complement and second gear, and slidably engaged with the first gear, wherein the first complement and second gear are configured to move continuously between a first position corresponding to the maximum flow rate and a second position corresponding to the zero flow rate; a fixed follower sealably engaged with the second complement and slidably engaged with the second gear; and a timing gear configured to rotate in correspondence with said first driven gear.
 2. The pump of claim 1 , further comprising: a drive shaft carrying said first driven gear in driving relation.
 3. The pump of claim 2 , further comprising: an idler axle carrying said second gear.
 4. The pump of claim 3 , wherein the timing gear is spaced axially from the first driven gear by the stationary follower.
 5. The pump of claim 4 , wherein the stationary follower further comprises: a sleeve center positioned to cooperate with the second complement.
 6. The pump of claim 5 , wherein the sleeve center has an axial length at least equal to a thickness of the second complement.
 7. The pump of claim 6 , wherein the movable follower further comprises: a sleeve positioned to slide axially over said sleeve center in a sealed relation, further adapted to travel with the movable follower.
 8. The pump of claim 7 , further comprising a pump chamber having a continuously variable length defined by a distance between the first and second complements.
 9. The pump of claim 8 , wherein said pump chamber length varies continuously between a maximum length corresponding to the length of said first driven gear less the length of the first compliment and a minimum length, including zero, corresponding with said zero flow rate.
 10. The pump of claim 9 , further comprising: an adjuster configured to continuously vary the length of said pump chamber between said maximum length and said minimum length.
 11. The pump of claim 10 , wherein said adjuster comprises: a mechanical linkage configured to displace the movable follower.
 12. The pump of claim 10 , wherein said adjuster comprises: a fluid applied to exert a differential pressure between a proximal piston face and a distal piston face, wherein the proximal piston face comprises a proximal end of the follower and a proximal end of the first complement, and wherein the distal piston face comprises a distal end of said first driving gear and a distal end of said sleeve.
 13. The pump of claim 10 , further comprising a metering valve found between the movable follower and an output port, wherein said metering valve operates at reduced chamber length.
 14. The pump of claim 11 , wherein the timing gear is configured to reduce energy applied to fluid within the housing.
 15. An improved pump, having axially translatable gears, to reduce energy applied to a working fluid during conditions of reduced pump output and full drive shaft speed, the improvement comprising: a pump chamber comprising a sleeve and having a variable length to proportionally control pump output, the length variable between a maximum length and a minimum length, the minimum length corresponding to an effectively zero pump output; the sleeve forming a pumping seal with a gear when the pump is configured to produce an output flow; a timing arrangement adapted to keep a plurality of gears in constant synchronization, whether the gears are engaged or fully disengaged; and an adjuster to vary the chamber length between the maximum and the minimum.
 16. The pump of claim 15 , wherein the chamber length is a distance between a proximal seal and a distal seal.
 17. The pump of claim 16 , wherein: the distal seal comprises a stationary follower to form an effective axial seal with an axially fixed gear; and the proximal seal comprises a movable follower to form an effective axial seal with an axially translating gear.
 18. The pump of claim 17 , wherein the stationary follower comprises a portion of a gear complement, a sleeve center, and a housing bridge element.
 19. The pump of claim 15 , wherein the sleeve is cantilevered from a movable follower and journaled in a housing for axial translation.
 20. The pump of claim 19 , wherein a sleeve center, coaxial with the sleeve, axially spaces a timing gear from another gear.
 21. The pump of claim 15 , wherein the adjuster comprises a mechanical linkage structured to translate a movable follower.
 22. The pump of claim 15 , further comprising a metering valve between a movable follower and an output port, the metering valve operable during conditions of reduced chamber length.
 23. The pump of claim 15 , the timing arrangement comprising: a timing gear maintained in meshing agreement with a first gear, and axially spaced apart from the first gear.
 24. The pump of claim 15 , wherein the adjuster comprises: a working fluid applied to exert a differential pressure between a proximal piston face and a distal piston face; the proximal piston face comprising a proximal end of a follower and a proximal end of a complement; and the distal piston face comprising a distal end of a gear and a distal end of the sleeve.
 25. The pump of claim 24 , wherein the working fluid is pressurized by a secondary pump between a gear and a timing gear.
 26. A method to vary a fluid output rate, between a maximum rate and essentially zero, during a constant operational speed for a positive displacement pump, the method comprising: providing a pump comprising: gears, including first and second pump gears, and a timing gear to maintain synchronization between the pump gears; with the first pump gear in pump sealing relation to a sleeve cantilevered from a movable follower; the pump gears arranged for meshing engagement and mounted for relative axial translation between a position of maximum length engagement to complete disengagement; and axially translating the second pump gear relative to the first pump gear such that the engagement length therebetween correspondingly changes between a maximum length and zero.
 27. The method of claim 26 , wherein the axial translation is effected by a mechanical linkage element arranged to translate the movable follower. 